1. Field of the Invention
The present invention relates generally to polybenzimidazoles. In particular, it relates to polybenzimidazoles prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl)benzimidazole monomers with activated aromatic dihalides or activated dinitro compounds.
2. Description of the Related Art
Polybenzimidazoles (PBIs) are heterocyclic macromolecules commonly prepared by the condensation reaction of an aromatic bis(o-diamine) with an aromatic diacid or derivative thereof. These polymers possess high thermal, thermooxidative, and chemical stability; good mechanical properties; and excellent flame resistance, making them high-performance/high-temperature materials which are attractive for use in harsh environments. However, despite these properties, the processing of these polymers is somewhat difficult.
Buckley et al (Encyclopedia of Polymer Science and Technology, Volume 11, 2nd Ed., 1988, p.572) review polybenzimidazoles. They specifically review poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole], which is commercially available primarily from Hoechst-Celanese Corporation. The processing of this material involves two steps: the formation of a foam which must be ground into a powder and reheating of the PBI powder. This polymer is mainly used in the formation of fibers because it is not very soluble in solvent. For example, in order to dissolve the PBI in dimethylacetamide (DMAc), both the solvent and the polymer had to be heated under pressure. The glass transition temperatures (Tg) of this polymer is 435.degree. C. Because of this high Tg, the polymer is difficult to compression and injection mold.
Several methods have been used to prepare PBIs. Brinker and Robinson (U.S. Pat. No. 2,895,948) synthesized PBIs by reacting aliphatic dicarboxylic acids with aromatic bis(o-diamine)s. Vogel and Marvel (Journal of Polymer Science, 50, 511 (1961)) formed PBIs from the melt condensation of aromatic bis(o-diamine)s with aromatic diacids or derivatives thereof. Iwakura et al (Journal of Polymer Science, Part A, 2, 2605, (1964)) prepared PBIs in polyphosphoric acid. Hedberg and Marvel (Journal of Polymer Science, Polymer Chemistry, 12, 1823 (1974)) formed PBIs in sulfolane or diphenylsulfone from aromatic bis(o-diamine)s and aromatic diacids or derivatives thereof. Another preparative route by Higgins and Marvel (Journal of Polymer Science, Part A-1, 8, 171 (1970)) involves the reaction of aromatic bis(o-diamines)s with the bis(bisulfite adduct)s of dialdehydes. Packham et al (Polymer, 10 (12), 923 (1969)) formed PBIs from the alkoxide catalyzed reaction of aromatic bis(o-diamine)s with dinitriles. None of these methods teach the preparation of PBIs by the reaction of di(hydroxyphenyl)benzimidazole monomers with activated aromatic dihalide or dinitro compounds in the presence of an alkali metal base.